The present invention relates to a method for calibrating a spatial position and/or orientation of at least one surgical referencing unit of a surgical navigation system fitted with at least one inertial sensor in relation to a spatial coordinate system.
The present invention also relates to a surgical calibration device for calibrating a spatial position and/or orientation of at least one surgical referencing unit of a surgical navigation system fitted with at least one inertial sensor in relation to a spatial coordinate system.
Known surgical navigation systems comprise referencing units that either reflect electromagnetic radiation emitted by a detection device of the navigation system or themselves emit electromagnetic radiation that can be received by the detection device. In alternative embodiments, it is also known to use ultrasound instead of electromagnetic radiation. A spatial position of the referencing unit can be determined absolutely in relation to a coordinate system defined by the detection device by means of transit-time measurements with navigation systems based on ultrasound that is emitted and received again by the detection device. A determination of position and/or orientation with navigation systems emitting and/or receiving electromagnetic radiation is based on field changes. Moreover, it is also possible to detect position or orientation changes by purely video-optical means. Navigation systems that perform a position and/or orientation detection purely by means of imaging processes are used for this purpose.
The aim of using a navigation system is to track spatial movements of the referencing units. As described above, absolute position data and/or orientations of the referencing unit can be determined by means of known navigation systems for this purpose. A movement path of the referencing unit can be reconstructed or computed on the basis of the determined position data and/or orientations.
However, if a surgical referencing unit is fitted with at least one inertial sensor, then a determination of position and/or orientation data of the referencing unit in any desired coordinate system can no longer occur directly, but must be computed on the basis of position and/or orientation changes. The reason for this, amongst other things, is that inertial sensors are sensors, with which forces and/or accelerations acting on them as a result of position and/or orientation changes can be measured. If more than one inertial sensor is used, in particular when six inertial sensors are used, three of which can detect the forces and/or accelerations in three mutually linearly independent directions and three of which can detect rotational angle changes around three mutually linearly independent axes, then position and/or orientation changes can also be determined uniquely in three-dimensional space on the basis of forces and/or accelerations acting on the inertial sensors.
Since no absolute position and/or orientation data can be determined directly with inertial sensors, it is therefore an object of the present invention to propose a method and a device of the above-described type, with which it is possible to reference or calibrate the at least one referencing unit in a predefined spatial coordinate system.